modify ups.py for python < 2.7 support

Add in a try/except block to catch errors generated by running python < 2.7:

$ ./test.py
Traceback (most recent call last):
  File "./test.py", line 338, in <module>
    TestUPS()
  File "./test.py", line 55, in TestUPS
    response = u.label(intl_packages, shipper, r, ups.SERVICES[9][0], ups.PACKAGES[5][0], validate, [ 'test@mytrashmail.com '], create_commercial_invoice=True, customs_info=products)
  File "/python-ship/ups.py", line 319, in label
    shipment = self._create_shipment(client, packages, shipper_address, recipient_address, box_shape, create_reference_number=create_reference_number, can_add_delivery_confirmation=delivery_confirmation)
  File "/python-ship/ups.py", line 147, in _create_shipment
    package = client.factory.create('{}:PackageType'.format(namespace))
ValueError: zero length field name in format